Orthognathic surgery now makes it possible to correct dental and facial deformities that previously could not be treated. The goal of this continuing project is to evaluate the morphologic, clinical, technical and physiologic response factors that determine stability of results from this surgical-orthodontic treatment. Utilizing existing computer data base information from the first phases of this project along with data from new patients, we will test specific hypotheses to explore the relationships of the patient's original dentofacial deformity and clinical treatment procedures to physiologic adaptation and morphologic stability followng treatment. In the present project period, emphasis will be placed on documenting long term (5 year) stability or morphologic changes; further exploration of the relationship between the physiologic variables of lip pressure, nasal resistance and respiratory mode to morphologic stability or relapse tendencies; tests of association between mode to morphologic stability or relapse tendencies; tests of association between clinical variables (direction and nagnitude of jaw movement, graft material, type of incision, etc.) and morphologic stability; clarifying the effects of various orthognathic surgery procedures on jaw function and indicated by temporomandibular joint adaptation and by occlusal force magnitude and direction; evaluating the effects of rigid fixation with screws and/or small bone plates on short and long term stability; and testing the hypothesis that relocating the chin (genioplasty) via lower border osteotomy significantly alters the balance between tongue and lip pressures across the lower incisors and thereby changes the stable position of these teeth. Research of this type to clarify physiologic adaptation and morphologic stability following surgery is important to improve furture treatment. The data also can provide a better understanding of the etiology of facial deformity problems by illustrating the effect of changes in humans.